1. Field of the Invention
Embodiments of the present invention relate generally to an imaging sensor, an image reading device, an image forming apparatus, and an alignment method of an imaging sensor.
2. Description of the Related Art
Some type of scanners includes a photoelectric conversion element which conducts photoelectric conversion of light reflected from an original document and outputs an analog image signal, an analog processing unit which performs processing, such as A/D (analog-to-digital) conversion, on the analog image signal to obtain digital image data, an image correcting unit which performs various corrections on the digital image data, and an image transfer unit which transfers the image data downstream by LVDS (low voltage differential signaling) transmission or the like.
As the photoelectric conversion element, CCD (charge coupled device) has conventionally been widely used. However, recent demands for reducing power consumption turn spotlight on CMOS (complementary metal oxide semiconductor) linear image sensors. CMOS linear image sensors are analogous to CCDs in conducting photoelectric conversion of incident light using photodiodes (light-receiving elements).
However, unlike a CCD which transfers charges using a shift register and, after transferring the charges, conducts charge-voltage conversion in a change detecting unit, a CMOS linear image sensor converts charges in a charge detecting unit in a pixel into a voltage signal and outputs the voltage signal downstream via a switch and an analog bus after buffering the voltage signal in an output buffer. CMOS linear image sensors are known to consume less power than CCDs because a CMOS linear image sensor requires only the switch as a load to be driven.
Meanwhile, Japanese Laid-open Patent Application No. 2006-229935 discloses an image sensor including a pixel array unit made up of multiple unit pixels arranged in a matrix array and multiple power supply lines arranged on the pixel array unit to supply a power supply voltage to the unit pixels. The power supply lines are arranged in a direction, in which the pixel array unit outputs video signals and which intersects a scan direction.
However, conventional CMOS linear image sensors are disadvantageous for the reason described below. Power supply lines are formed to extend in a direction in which rows of pixels of respective colors lie. A power supply voltage is supplied to one end of each of the pixel rows of the respective colors. Accordingly, drop in the power supply voltage supplied to light-receiving elements undesirably increases with the distance from the one end of the pixel row and, as a result, unwanted homogeneity is developed in image data.
Therefore, it is desirable to provide an imaging sensor an image reading device, and an image forming apparatus capable of preventing variation of power supply voltage supplied to light-receiving elements, the variation depending on a position of a pixel of each color.